# CHEM106: Physical Chemistry II

Unit 3: Practical Problems in Quantum Mechanics

In this unit, you will begin to use the equations and principles of quantum mechanics to solve some simple problems, involving relatively simple mathematics.  Although the examples presented here involve mostly “imaginary” particles in ideal quantum systems, these examples will serve as an introduction to quantum mechanical calculations.  The principles learned using these ideal systems (e.g., particle in a box) can be used later in “real” systems (molecules).  As the system under study becomes more and more complex, you will learn how to adopt certain techniques of approximation to simplify your calculation and still obtain fairly accurate results.

This unit will take you 16.5 hours to complete.

☐    Subunit 3.1: 6 hours

☐    Subunit 3.2: 6 hours

☐    Subunit 3.3: 4.5 hours

Unit3 Learning Outcomes
Upon successful completion of this unit, the student will be able to: - Explain the difference between classical and quantum mechanics. - Apply the Schrodinger equation to solve the “particle in a box” problem. - Describe quantum phenomena such as tunneling and barrier penetration. - Derive energy levels for quantized systems, such as a harmonic oscillator. - Describe the molecular vibrations in terms of simple systems, such as a spring. - Describe the difference between harmonic and anharmonic oscillators. - Transform equation from Cartesian coordinates to polar and/or spherical coordinates. - Solve the Schrodinger equation in polar and spherical coordinates. - Explain how the angular momentum is a conserved quantity. - Describe the motion of a particle around a ring or on the surface of a sphere. - Apply angular momentum operators to solve “spin” problems.

3.1 Particle in a Box (Translational Motion)   - Reading: Boston University: Professor Dan Dill’s “Analytic Solution of the Schrödinger Equation: Particle in a Box” and “Example of One-Dimensional Quantum System” Link: Boston University: Professor Dan Dill’s “Analytic Solution of the Schrödinger Equation: Particle in a Box” and “Example of One-Dimensional Quantum System” (PDF)

Instructions: Please click on the first and second links above and scroll down the webpage to the italic headings, “Particle in a Box” and “Example of One-Dimensional Quantum System.”  To open each set of notes, click on the hyperlink next to these italicized headings.  A PDF file of each section will open up.  Read each PDF file in its entirety (7 pages and 6 pages, respectively).  While reading the material, repeat each mathematical derivation on scratch paper.  Studying this resource should take approximately 2 hours to complete.  Note that this reading also covers the material you need to know for subunits 3.1.1–3.1.4.

• Reading: The Chemistry Hypermedia Project’s “Particle in a Box” Link: The Chemistry Hypermedia Project’s “Particle in a Box” (HTML)

Instructions: Please click on the link and read the Chemistry Hypermedia Project webpage, which provides a glance of the particle in a box problem.  While reading the material, repeat each mathematical derivation on scratch paper.  Studying this resource should take approximately 1.5 hours to complete.  Note that this reading also covers the material you need to know for subunits 3.1.1–3.1.4.

• Reading: Everyscience.com’s “Particle in a Two-Dimensional Box” Link: Everyscience.com’s “Particle in a Two-Dimensional Box” (HTML)

Instructions: Please click on the link and read the entire webpage, which presents the problem in 2D.  While reading the material, repeat each mathematical derivation on scratch paper.  Studying this resource should take approximately 1 hour to complete.  Note that this reading also covers the material you need to know for subunits 3.1.1–3.1.4.

• Web Media: Kansas State University: Physics Education Research Group’s “Visual Quantum Mechanics – Quantum Tunneling” Link: Kansas State University: Physics Education Research Group’s “Visual Quantum Mechanics – Quantum Tunneling” (Adobe Shockwave)

Instructions: Please click on the link above and follow the steps on the webpage to simulate tunneling.  Studying this resource should take approximately 1 hour to complete.  Please note that this program requires Adobe Shockwave.  If you do not already have Shockwave, you can download a free version here.  Note that this reading also covers the material you need to know for subunits 3.1.1–3.1.4.

• Web Media: YouTube: Praba Siva’s “Schrodinger Equation – For Particle in a 1 D, 2D, 3D Box” and David Colarusso’s “What Is Quantum Tunneling?” Links: YouTube: Praba Siva’s “Schrodinger Equation – For Particle in a 1 D, 2D, 3D Box” and David Colarusso’s “What Is Quantum Tunneling?” (YouTube)

Instructions: Please click on the links above, and watch these videos.  These are short videos that explain how to solve the Schrodinger equation for one-, two-, and three-dimensional systems (Praba Siva’s video) and explain the phenomenon of quantum tunneling (David Colarusso’s video).  Note that these videos also cover the material you need to know for subunits 3.1.1–3.1.4.  Studying these resources should take approximately 0.5 hours to complete.

• Assessment: The Saylor Foundation’s “Assessment 5” Link: The Saylor Foundation’s “Assessment 5” (DOC)

Instructions: Complete the attached assessment questions to check your understanding of the material covered thus far. Once you have completed the assessment, you may check your answers against the “Answer Key” (DOC).

Completing this assessment should take approximately 1 hour.

3.1.1 Particle in a One-Dimensional Box   Note: This topic is covered by the readings assigned beneath subunit 3.1.  In particular, please focus on Chemistry Hypermedia Project’s “Particle in a Box” and Professor Dan Dill’s “Analytic Solution of the Schrödinger Equation: Particle in a Box” to learn about one-dimensional quantum mechanical systems.

3.1.2 Example of One-Dimensional Quantum Systems   Note: This topic is covered by the readings assigned beneath subunit 3.1.  In particular, please focus on Professor Dan Dill’s “Example of One-Dimensional Quantum System” to learn about the behavior of quantum particles “confined” into quantum wells with different energy barriers.

3.1.3 Barrier Penetration and Tunneling   Note: This topic is covered by the readings assigned beneath subunit 3.1.  In particular, please focus on David Colarusso’s “What Is Quantum Tunneling?” and Professor Dan Dill’s “Example of One-Dimensional Quantum System” to learn about the unique phenomenon of quantum tunneling.

3.1.4 Particle in a 2D or 3D Box   Note: This topic is covered by the readings assigned beneath subunit 3.1.  In particular, please focus on Everyscience.com’s “Particle in a Two-Dimensional Box” and Praba Siva’s web media, “Schrodinger Equation – For Particle in a 1 D, 2D, 3D Box,” to learn about the behavior of quantum particles in more than one dimension.

3.2 Vibrational Motion   - Reading: Everyscience.com’s “Molecular Vibrations” and “Anharmonic Oscillator” Links: Everyscience.com’s “Molecular Vibrations” and “Anharmonic Oscillator” (HTML)

Instructions: Please click on the “Molecular Vibrations” and “Anharmonic Oscillator” links and read these webpages in their entirety.  While reading the material, repeat the mathematical derivation of the vibrational terms.  Studying this resource should take approximately 1.5 hours to complete.  Note that these readings also cover the materials you need to know for subunits 3.2.1–3.2.3.

• Reading: Boston University: Professor Dan Dill’s “Harmonic Oscillator” Link: Boston University: Professor Dan Dill’s “Harmonic Oscillator” (PDF)

Instructions: For Professor Dill’s notes, please click on the link above, scroll down the webpage to the italic heading, “Harmonic Oscillator,” and click on the hyperlink to the PDF next to the heading.  Read the entire PDF (18 pages).  While reading the material, repeat the mathematical derivation of the harmonic potential and understand the difference between harmonic and anharmonic vibrational terms.  Studying this resource should take approximately 3 hours to complete.  Note that this reading also covers the materials you need to know for subunits 3.2.1–3.2.3.

• Web Media: YouTube: Indian Institute of Technology, Madras: Professor K. Mangala Sunder’s “Lecture 4 Harmonic Oscillator and Molecular Vibration” Link: YouTube: Indian Institute of Technology, Madras: Professor K. Mangala Sunder’s “Lecture 4 Harmonic Oscillator and Molecular Vibration” (YouTube)

Instructions: Please click on the link above, and watch the entire video.  While watching the video, repeat the mathematical derivation following the professor’s notes on the board.  Studying this resource should take approximately 1.5 hours to complete.  Note that this video lecture also covers the material you need to know for subunits 3.2.1–3.2.3.

• Assessment: The Saylor Foundation’s “Assessment 6” Link: The Saylor Foundation’s “Assessment 6” (DOC)

Instructions: Complete the attached assessment questions to check your understanding of the material covered thus far. Once you have completed the assessment, you may check your answers against the “Answer Key” (DOC).

Completing this assessment should take approximately 1 hour.

3.2.1 Overview of Molecular Vibrations   Note: This subunit is covered by the readings assigned beneath subunit 3.2.  In particular, please focus on Everyscience.com’s “Molecular Vibrations” to have an overview of molecular vibrations.

3.2.2 Harmonic Oscillator   Note: This subunit is covered by the readings assigned beneath subunit 3.2.  In particular, please focus on  Professor Dan Dill’s “Harmonic Oscillator” and Professor K. Mangala Sunder’s “Lecture  4 Harmonic Oscillator and Molecular Vibration” to learn how harmonic oscillators can be used to model molecular vibrations.

3.2.3 The Anharmonic Oscillator   Note: This subunit is covered by the readings assigned beneath subunit 3.2.  In particular, please focus on Everyscience.com’s “Anharmonic Oscillator” to learn how the anharmonic oscillator is a better representation of molecular vibration as it allows bond dissociation at high vibrational excitations.

3.3 Angular Momentum and Rotational Motion   - Web Media: bpReid-Software for Science and Mathematics’ “Particle on a Sphere – Spherical Harmonics” Link: bpReid-Software for Science and Mathematics’ “Particle on a Sphere – Spherical Harmonics” (HTML)

Instructions: Please click on the link above, and complete the exercises on the webpage to simulate the spherical harmonics.   Please note that this program requires Oracle’s Java Runtime.  If you do not already have it, you can download a free version here.  Studying this resource should take approximately 0.5 hours to complete.  Note that this resource also covers the material you need to know for subunits 3.3.1–3.3.5.

Instructions: Please click on link to learn about polar coordinates.  In this resource, it is important that you learn how to transform Cartesian coordinates into polar coordinates.  Studying this resource should take approximately 0.5 hours to complete.  Note that this reading also covers the material you need to know for subunits 3.3.1–3.3.5.

• Reading: Boston University: Professor Dan Dill’s “A Little Bit of Angular Momentum,” “Angular Motion in Two-Components Systems,” and “Particle Moving on a Ring” Link: Boston University: Professor Dan Dill’s “A Little Bit of Angular Momentum”,  “Angular Motion in Two-Components Systems”, and “Motion of a Particle on a Ring” (PDF)

• Reading: University of California Davis: UC Davis ChemWiki’s “Particle on a Ring” and “Particle on a Sphere” Links: University of California Davis: UC Davis ChemWiki’s “Particle in a Ring” and “Particle in a Sphere” (HTML)

Instructions: Please click on the UC Davis ChemWiki links for a quick overview of a particle moving in a ring and in a sphere.  Studying these resources should take approximately 0.5 hours to complete.  Note that these readings also cover the material you need to know for subunits 3.3.1–3.3.5.

Also Available in:
HTML transcript, Mp3 audio, Mp4 video, Adobe Flash video from Open Yale Courses

Instructions: Please click on the link above, and watch the video.  You can focus on the lecture portion starting from approximately minute 12:40 to learn about the quantum motion of a particle on a ring.  Studying this resource should take approximately 1 hour to complete.

• Assessment: The Saylor Foundation’s “Assessment 7” Link: The Saylor Foundation’s “Assessment 7” (DOC)

Instructions: Complete the attached assessment questions to check your understanding of the material covered thus far. Once you have completed the assessment, you may check your answers against the “Answer Key” (DOC).

Completing this assessment should take approximately 1 hour.

3.3.1 Angular Momentum   Note: This subunit is covered by the readings assigned beneath subunit 3.3.  In particular, please focus on Professor Dan Dill’s “Angular Motion in Two-Components Systems” to learn about angular momentum.

3.3.2 Polar and Spherical Coordinates   Note: This subunit is covered by the readings assigned beneath subunit 3.3.  In particular, please focus on and Everyscience’s “Polar Coordinates” to learn how to transform Cartesian coordinates into polar and spherical coordinates.

3.3.3 Particle on a Ring   Note: This subunit is covered by the readings assigned beneath subunit 3.3.  In particular, please focus on Professor Dan Dill’s “Particle Moving on a Ring,” ChemWiki’s “Particle on a Ring,” and the web media Yale courses, “Quantum Mechanics III,” from approximately minute 12:40, to learn about the quantum motion of a particle on a ring.

3.3.4 Particle on a Sphere   Note: This subunit is covered by the readings assigned beneath subunit 3.3.  In particular, please focus on UC Davis ChemWiki’s “Particle on a Ring and Particle on a Sphere” and on the Web Media: “Particle on a Sphere – Spherical Harmonics.”

3.3.5 Spin   Note: This subunit is covered by the readings assigned beneath subunit 3.3.  In particular, please focus on Professor Dan Dill’s “A Little Bit of Angular Momentum” to learn about spin angular momentum.